Alternation of generations is a term that describes the life cycle of most plants and some algae. The term generations is misleading since it refers to two different phases that make up a single life cycle.
In one phase, the plant is known as a gametophyte or gamete-bearing plant and produces sex cells called gametes. Gametophytes can produce male sperm cells, female egg cells, or both. When a sperm cell and an egg cell unite, they form a zygote (fertilized egg). The zygote develops into the next phase of the reproductive cycle. In this phase, the plant is known as a sporophyte or spore-bearing plant and produces reproductive cells called spores. Then spores develop into gamete-producing plants, and the cycle begins again.
In most plants, the gametophyte and the sporophyte differ in size and appearance. For example, the phase that people recognize in ferns is the sporophyte. The familiar phase of mosses is the gametophyte. The sporophyte is the familiar phase of all flowering and cone-bearing plants.
